The present invention relates to a feeder device for feeding yarns having elastic characteristics for a knitting machine, in particular a hosiery knitting machine.
In the processing of hosiery, in order to give elastic characteristics to the product, it is known to insert an elastic yarn in correspondence of certain stitch courses, with said yarn having elastic characteristics being knitted between the stitch loops. According to the shape of the product, it may become necessary to feed amounts of yarn which are different from course to course, e.g., by progressively decreasing or increasing the amount of yarn fed per each stitch course.
The feeding of a yarn having elastic characteristics is generally carried out by means of a feeder roll, kept pressed against the face of a revolving disk, the revolution speed of which depends on the revolution speed of the machine, with the yarn running between the roll and the disk. In order to control the amount of yarn fed per each unit time, the roll is shifted along the surface of the disk according to a radial direction of the same disk, i.e., parallel to the axis of the roll, so as to vary the peripheral speed of the roll, as well as the radial distance of the yarn from the axis of revolution of the disk, which continues to revolve at a speed derived from the speed of the machine.
Such a feeder device is capable of delivering to the machine one elastic yarn only. In case feeding a plurality of elastic yarns is desired, whether with one elastic yarn feed, or a plurality of elastic yarn feeds, a plurality of devices of this kind have to be provided, with several problems consequently arising.
Besides the problems of overall dimensions and of cost, which are not negligible, the problem exists that a plurality of yarns have to be fed at the same speed and under the same tension, otherways in the finished product more and less tensioned yarns would be contained, with a considerable worsening in product quality. With a plurality of devices of the above stated type, identical conditions of feeding of the respective yarns cannot be secured.